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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

hello
last night when i was driving at around 4-5k revs the engine died and a piston or rod went through the engine block. the car is a 525i m54 double vanos engine with 150k miles on it.
my question is what caused this , i know i had a compression problem on cyl 6 it was 9 and the other cylinder where 11.5 , could this be the cause
and what do you think i should buy another m54b25 engine or a m54b30
is the swap easy , on realoem it says that the clutch is different and the gearbox also

Are you sure that rod/piston went through the block? Or are you just guessing, since it won't start? Catastrophic damage like that is quite rare on e39. Only thing that comes to mind is that the engine ingested large amount of water, hence hydrolocked. Swapping another m54b25 engine is straightforward, you just need to have the tools and know what your doing.

These should help:
- Summary advice to provide users who suspect a major engine repair due to overheating (1) (2) (3) (4) & how to test an engine for a blown head gasket, cracked heads, a warped block, stripped head bolt threads, cam seizures, contaminated bearings, coolant hydrolock, or piston, ring, or valve damage (1) (2) & what are the major factors in deciding whether to rebuild the engine, replace the engine, or sell the car (1) & a DIY for replacing the I6 M54 head gasket (1) (2) & replacing the V8 M62TU head gasket (1) & why these engines are so prone to heat-related damage in the first place (1) & welding the crack between cylinder #3 and the water jacket on the exhaust side (1) & what engine swaps are most recommended (1) (2) (3) & where to obtain a new or rebuilt head (1) replacement short block or long block (1) (2) & how to lift & remove the engine (1) & the most recent real-world results from the last 50 people faced with similar blown engine problems from which this advice came from (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48) (49) (50)

no , i had that problem 2 years ago , could it be a result of that , but now its dry
when i get a new engine will see what realy happened

No it can't be a result of that. Water under the drivers side cabin air filter can be sucked in the engine via vacuum hose that is connected to the brake booster. If engine sucks up enough water the engine will immediately be destroyed. Did you have enough engine oil?

got a closer look at the engine has 4 holes in it and one in the oil pan
got a question for you , in one of the holes , near the gearbox there is a plastic rod stinking out of it , what could it be?? part of the gearbox??

is quite interesting...I see a piece of a flywheel which isn't an internal part this is external to the engine i tself...I would be very interested to see...

And in 36 years in the auto industry I've NEVER seen a piston go through an engine...NEVER...now I have seen quite a few broken rods go through a block...and if the rod goes through some are actually repairable...

There are Corvettes in Europe, it's just that the Z06 LS7 probably was not sold there. But, since they are not plentyful, it's a little bit more difficult to source an LSx with a manual transmission for any reasonable money.